Apparatus for die casting ferrous metals

ABSTRACT

In a die casting machine for injection moulding metals of high melting points into a metal mold by means of an injection cylinder connected to the metal mold at one end and a plunger inserted into the injection cylinder from the opposite end, the injection cylinder comprises an outer cylindrical sleeve of high heat conductivity and is provided with a molten metal pouring opening near said opposite end and an inner cylindrical lining removably fitted in the outer sleeve, the inner lining including a plurality of sections of short axial length which are clamped together into the cylindrical lining, one of the sections positioned at the opposite end being provided with a molten metal pouring opening aligned with that of the outer sleeve.

Unite States Miura et a1.

atent APPARATUS FOR DIE CASTING FERROUS METALS [72] Inventors: Yasushi Miura; Nobuo Kashiwagi; Zenichi Mochizuki, all of Numazu-shi, Shizuokaken, Japan [73] Assignee: Toshiba Kikai Kabushiki Kaisha, Chuoku, Tokyo-to, Japan [22] Filed: June 13, 1969 [21] Appl. No.1 832,989

[52] U.S.Cl ..l64/312,164/314, 164/4, 164/136, 164/113, 266/43 [51] Int. Cl ..B22d 17/04 [58] FieldotSearch ..164/3l2,314, 113,303

[56] References Cited UNITED STATES PATENTS 3,015,849 1/1962 Mittelstadt et al. ..164/3l4X 3,208,113 9/1965 Bennett ..164/312 3,447,593 6/1969 Nyselius ..164/312 3,058,179 10/1962 Cannon ..164/314 3,315,315 4/1967 Truilzi .164/113 X 3,516,480 6/1970 Woltering ..164/312 3,515,203 6/1970 Parlantiet al ..164/312 as Il Primary Examiner-J. Spencer Overholser Assistant Examiner-V. K. Rising Attorney-Wenderoth, Lind & Ponack [5 7] ABSTRACT In a die casting machine for injection moulding metals of high melting points into a metal mold by means of an injection cylinder connected to the metal mold at one end and a plunger inserted into the injection cylinder from the opposite end, the injection cylinder comprises an outer cylindrical sleeve of high heat conductivity and is provided with a molten metal pouring opening near said opposite end and an inner cylindrical lining removably fitted in the outer sleeve, the inner lining including a plurality of sections of short axial length which are clamped together into the cylindrical lining, one of the sections positioned at the opposite end being provided with a molten metal pouring opening aligned with that of the outer sleeve.

1 Claim, 8 Drawing Figures PATENTEDJUHN m2 SHEET 10F 2 YASUSHI MIURA,

NOBUO KASHIWAGI and ANGLE OF iNCLINATlON, e

, ZENICHI MOCHIZUKI,

INVENIOR BY AJJMJMJKZXLZ 41M ATTORNEY s This invention relates to a method and apparatus for die casting ferrous metals such as cast iron and steel.

When a high pressure die casting or injection moulding machine designed for die casting metals of low melting points such as aluminum, zinc or their alloys is used for ferrous metals having higher melting points, there arise a number of problems. More particularly, the conventional high pressure die casting machine for low melting point metals usually comprises a horizontal injection cylinder and a plunger or a piston movable therein. The cylinder is provided with an opening for receiving molten metal at one end thereof remote from a metal mould, and the plunger is operated to inject the molten metal into the metal mould under high pressure. Where the molten metal poured into the cylinder has a high melting point, the inner surface of the cylinder immediately beneath the opening becomes damaged due to heat shock of the molten metal poured into the cylinder. As above described, since the cylinder is horizontal, the distance in the cylinder over which the molten metal is driven by the plunger is relatively long, and the contact area between the molten metal and the plunger is wide. As a consequence, there is a tendency of forming a solidfied layer thus requiring higher injection pressure. This also causes deformation of the plunger cylinder, and die members.

Further, where a horizontal injection cylinder is used, and the molten metal partially fills the cylinder, slag floating on the upper surface of the molten metal contained in the cylinder may be entrained in the injected metal thus forming moulded products of non-uniform structure.

Another problem arises when ferrous metals are moulded by a die casting machine designed for metals of low melting point. Such metals of low melting points as aluminum, zinc or their alloys are usually injected under pressures ranging from 500 kg/cm to 600 kg/cm Such high pressures are advantageous for non-ferrous metals of low melting points because of their high plastic fluidity at elevated temperatures, thus decreasing blowholes and increasing the density and mechanical strength of moulded products.

However, in the case of ferrous metals, especially cast iron, plastic fluidity is very small so that the deformation coefficient before breakage is only 1/2000 of that of aluminum. On the other hand, ferrous metals are readily chilled to provide dense structures. Thus ferrous metals have physical characteristics quite different from those of non-ferrous metals. For this reason, high injection pressures adequate for non-ferrous metal can not be used for injection moulding ferrousmetals. Rather such high pressures hasten damage of metal moulds, and thus require bulky and rigid construction of the injection moulding machines.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide an improved die casting machine wherein damaged'portions of the injection cylinder can be readily replaced. 7

Another object of this invention is to provide a novel die casting machine by which blowholes or non-uniform structure of moulded products can be eliminated.

A further object of this invention is to provide a method of die casting ferrous metals under low pressures.

According to one aspect of this invention, an injection cylinder of a die casting machine is lined with a plurality of sections or sleeves of short axial length which are fitted in an outer sleeve of high heat conductivity. With this construction it is possible to replace damaged sections alone without replacing the entire cylinder.

According to another aspect of this invention, in order to prevent entrainment of slag and air bubbles, the injection cylinder is positioned at an angle to the horizontal.

According to still another aspect of this invention ferrous metals are die cast under low pressures, of the order of from to 100 kg/cm".

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings FIG. 1 shows a diagrammatic sectional view of a die casting machine constructed according to this invention;

FIG. 2 is a perspective view of an experimental device for measuring the heat insulating effect of molten metal;

FIG. 3 is a longitudinal sectional view of a cylindrical container shown in FIG. 2;

FIG. 4 is a plot of a heat insulating characteristic of the experimental device shown in FIGS. 3 and 4; and

FIG. 5 to 8 show successive steps of die casting utilizing an inclined injection cylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the accompanying drawing, an injection cylinder 10 of a die casting machine comprises an outer cylinder 11, a sleeve 12 of a metal of high thermal conductivity, such as copper, a lining consisting of a plurality of sleeves or sections 13, 14, 15, 16 and 17 removably fitted in the copper sleeve 12, said sleeves having split a short axial length and being clamped together by means of a clamping ring 18 and bolts 19. As shown, the injection cylinder 10 is disposed at an angle 0 with respect to the horizontal. A pouring opening 20 is formed near the outer end of the injection cylinder to pour molten ferrous metal 22 into a space defined by split sleeves 13 through 17. A plunger 21 is inserted in the cylinder to inject under pressure the molten metal 22 into a mould cavity 23 connected to the inner end of the injection cylinder, said cavity being defined by a movable die member 27 and a stationary die member 28.

In the injection cylinder, the inner surface thereof immediately beneath the pouring opening 20, in this embodiment the inner surface of the sleeve 13 is damaged most severely by the heat shock of the poured molten metal. The novel construction, however, permits easy renewal of such heavily damaged sleeve without the necessity of replacing the entire injection cylinder. Moreover, as the copper sleeve 12 enhances dissipation of heat both in the radial and axial directions, the temperature differentials between adjacent sleeves 13 through 17 are reduced thus alleviating damages caused by heat shock imparted to sleeves remote from the pouring opening 20. This means that, except for the sleeve 13 including the pouring opening 20, frequent renewal of other sleeves can be avoided. It was found that sleeves made of a molybdenum alloy and subjected to a special treatment could be used more than 1,000 times. Further, materials having excellent heat shock proof characteristics but which heretofore could not be used because of their brittleness, can be utilized, since according to this invention, sleeves 13 to 17 have short axial lengths and are covered by sleeve 12, propagation of cracks is effectively prevented. In the conventional die casting machine the inner end of the plunger 21 is made flat. However, as the peripheral portion of the inner end of the plunger is subjected to extraordinary high thermal stress due to contact thereof with the molten metal and hence is deformed or creates a heat check. Accordingly, the gap between the inner wall of the injection cylinder and the plunger tends to increase with the result that a portion of the molten metal enters into the gap to interfere with the smooth movement of the plunger. However, by forming the inner end of the plunger to have a spherical configuration as shown in FIG. 1, the angle of the peripheral portion of the inner end becomes an obtuse angle thus minimizing abnormal thermal stress.

Another feature of this feature of this invention lies in the inclined disposition of the injection cylinder 10. With the horizontal injection cylinder, the distance over which the molten metal is moved axially of the cylinder is large so that the molten metal forms a solidified layer in a short time which causes damage to the inner wall of the injection cylinder and the inner end of the plunger, thus decreasing their operating life. Moreover, where the molten metal partially fills the injection cylinder, slag and air above the surface of the molten metal are entrained in the moulded article to form blowholes,

cracks and non-uniform structure. However, with the inclined injection cylinder, the distance of movement of the molten metal in the injection cylinder is decreasing thus decreased, the above described difficulty. Moreover, the risk of entraining slag and gas can also be decreased, thus producing a product of uniform quality. Theoretically, as the ratio of the volume to the contact surface of the molten metal increases, thermal insulation of the molten metal is increased thus improving moldability thereof.

FIGS. 2 and 3 illustrate an experimental device for measuring the heat insulating effect of molten metal. The device shown in FIGS, 2 and 3 comprises a cylindrical container 31 for molten metal. The cylindrical container 31 corresponds to the injection cylinder 10 shown in FIG. 1 and is tiltably supported on a base 32, the angle of inclination 6 with respect to the horizontal being adjustable by means of a handle 33 attached to the container. As the angle of inclination is varied, the contact area between the molten metal 34 and the container 31 is varied. More particularly, as the angle of inclination 9 is increased, the contact area is decreased. Thus, after selecting a predetermined angle 6 molten metal 34 of a predetermined quantity and at a predetermined temperature was poured into the container and after a predetumined time interval, one of the end covers 35 is removed to measure the quantity W of solidified metal remaining in the cylinder. The result showed that as the quantity of the molten metal increases, the degree of temperature drop of the molten metal decreases. Thus, the heat insulation effect is increased with an increase in the angle of inclination 6 a curve shown in FIG. 4 shows a heat insulating characteristic of the molten metal of the experimental device shown in FIGS. 2 and 3. From this curve it will be clear that an inclined injection cylinder is more advantageous than a horizontal one.

The result of experiment shows that the angle of is preferably in a range of from to 45. Above 45, prior to the actuation of the plunger 21, a quantity of the molten metal 22 enters into the mould cavity thus disenabling the production of moulded articles of excellent quality. In order to prevent this difficulty, it is necessary to use an injection mechanism of more complicated construction. Moreover as the contact area between the molten metal in the injection cylinder and the plunger and cylinder 10 increases, cooling of the molten metal is enhanced and the operating life of the injection mechanism is decreased. In addition an excessively large angle of inclination requires higher injection pressure.

As shown in FIG. 1, with an inclined injection cylinder, before commencing the moulding operation, the inner end ofthe plunger 21 is separated from a pool of molten metal 22 in the cylinder 10, so that cooling of the molten metal can be reduced. Moreover, as the contact area between the molten metal and the injection cylinder is reduced, heat dissipation of the molten metal can also be reduced.

As described before, with a horizontal injection cylinder, contaminants or slag such as oxides of metal and non-metal or gas are entrained in the stream of the molten metal with the result that the mechanical strength and density of the moulded products are impaired. More particularly, during injection when the plunger is advanced at a high speed, the molten metal in front of the plunger is vigorously stirred to entrain said containants in the stream of the molten metal injected into the cavity ofa mould.

FIGS. 5 through 8 illustrate the advantage of the inclined injection cylinder 10. In the condition shown in FIG. 5, a portion of the molten metal is already in a gate 25, but the major portion of the molten metal 22 is contained in the injection cylinder and the slag 24 is floating thereon. Consequantly, as the plunger 21 is advanced at a high speed, while the slag is broken up into small pieces and admixed with the molten metal, it is retained in the injection cylinder until the cavity 23 of the mould is completed filled. In this manner, the quality of the moulded product can be improved.

Another feature of this invention lies in the method of die casting metals of high melting points, especially ferrous metals. Non-ferrous metals such as aluminum, zinc or their alloys are die cast under a relatively high pressure of the order of about 500 to 600 kg/cm (7,000 to 8,500 lbs/in). As such non-ferrous metals have high plastic fluidity at elevated temperatures, such high pressures are effective to improve the mechanical strength of the moulded products owing to the decrease in blowholes and increase in the density. However, as mentioned before, the plastic fluidity of ferrous metals, especially cast iron is very small and as they are chilled very easily, it is necessary to provide high strength by annealing. Due to these basic differences, it is not possible to inject ferrous metals under high pressures comparable with those for nonferrous metals. We have found that the pressure for die casting ferrous metal, particularly cast iron can be reduced to about 25 to kg/cm (355 lbs/in to 1,500 lbs/in which is only sufficient to fill the molten metal in the mould cavity and to prevent drawing, the range of injection pressure being determined according to the volume or surface area of the mould Thus, the quantity of molten metal to be moulded and the injection speed thereof increase with the volume of the mould and the time required for the molten metal to solidify increases. For this reason, the injection pressure can be decreased to about l/lO to l/20 of that required for die casting non-ferrous metals. It was found that products having complicated configurations such as gears, cast under an injection pressure of 45 kg/cm had smooth surfaces and all corners were completely filled. Whereas in products cast under a pressure of less than 20 kg/cm surface, rumples and incomplete filling at corner portions were noted.

Where an injection pressure of more than 200 kg/cm" was used, after several casting operations molten metal leaked through the gap between the stationary die 28 (see FIG. 1) and the injection cylinder 10, thus greatly deforming cast products.

Thus, in die casting ferrous metals in metal moulds, injection pressure ranging from 25 to 100 kg/cm prevents damage at gaps between the movable die 27 and ejection pins 26 (see FIG. 1), the joint between the stationary die 28 and the injection cylinder 10 and the joint between a core (not shown) and the base ofa metal mould can be prevented so that the operating life of the metal mould is elongated and fins on the moulded products are reduced, thus enabling the manufacture of die cast articles at a low cost.

We claim:

1. In a die casting machine for metals of high melting points comprising a metal mold, an injection cylinder connected to said metal mold at one end, and a plunger inserted into said injection cylinder through the opposite end thereof to inject under pressure molten metal into said mold, the improvement wherein said injection cylinder is inclined with respect to the horizontal such that said opposite end is maintained at a higher level than said one end of said injection cylinder, and said injection cylinder comprises an outer cylindrical sleeve of high heat conductivity and is provided with a molten metal pouring opening through said sleeve near said opposite end and an inner cylindrical lining removably fitted in said outer sleeve, said inner lining including a plurality of cylindrical sections of short axial length which are clamped together within said cylindrical inner lining, one of said sections positioned at said opposite end being provided with a molten metal pouring opening aligned with said pouring opening of said outer sleeve. 

1. In a die casting machine for metals of high melting points comprising a metal mold, an injection cylinder connected to said metal mold at one end, and a plunger inserted into said injection cylinder through the opposite end thereof to inject under pressure molten metal into said mold, the improvement wherein said injection cylinder is inclined with respect to the horizontal such that said opposite end is maintained at a higher level than said one end of said injection cylinder, and said injection cylinder comprises an outer cylindrical sleeve of high heat conductivity and is provided with a molten metal pouring opening through said sleeve near said opposite end and an inner cylindrical lining removably fitted in said outer sleeve, said inner lining including a plurality of cylindrical sections of short axial length which are clamped together within said cylindrical inner lining, one of said sections positioned at said opposite end being provided with a molten metal pouring opening aligned with said pouring opening of said outer sleeve. 